Multi-path wireless channels are capable of large channel capacities, and may be properly exploited through the use of a multiple-input-multiple-output MIMO communication system. A MIMO system employs multiple transmit antennas and multiple receive antennas. Standard IEEE 802.16e, sometimes referred to as Mobile Worldwide Interoperability for Microwave Access (Mobile WiMAX), supports MIMO antenna technology. Future wireless networks will also support MIMO antenna technology. For example, TGn Sync is a multi-industry group working to introduce a unified proposal for the next generation of high performance wireless networks. This proposal was developed under the guidelines of the IEEE Standards Association and submitted to the IEEE 802.1 In Task Group N (TGn). One of the goals of the TGn Sync proposal is to enable MIMO Spatial Division Multiplexing to enable reliable transmission speeds of up to 315 megabits per second (Mbps) with two antennas, and up to 630 Mbps with larger systems employing more than two antennas.
A MIMO communication system may take advantage of beamforming to not only increase the overall antenna gain, but also to reduce interference between the received multi-path signals at the receiver. Currently, two MIMO technologies are under consideration: open-loop and closed-loop technologies. It is found that closed-loop MIMO technology outperforms open-loop MIMO by 4 to 10 decibels (dB). A promising scheme for closed-loop MIMO technology is Singular-Value-Decomposition (SVD) transmit beamforming.
SVD beamforming is a powerful beamforming technique showing promising results in MIMO communication systems. SVD beamforming requires performing the singular value decomposition of a channel matrix, in which the channel matrix represents the physical channel, transmitters, and receivers. SVD beamforming generally requires performing an iterative algorithm by a circuit, in which the circuit may be a programmable circuit. Performing such an iterative algorithm consumes both die space and power.
Some existing receivers for open-loop MIMO technology employ minimum mean square error receivers, or zero-forcing receivers. These receivers solve a least-squares criterion. Often, a QR decomposition, or other type of decomposition employing a unitary transformation, is applied to solve the least-squares criterion. It would be desirable to utilize existing QR-decomposition circuits to perform the singular value decomposition of the channel matrix.